Various microlithography systems (especially such systems used for fabricating semiconductor devices) include at least one stage device that holds a lithographic substrate (e.g., resist-coated semiconductor wafer). If the system utilizes a pattern-defining reticle, then the system typically also comprises a “reticle stage” for holding the reticle. A stage device not only holds the respective object (reticle or substrate) but also facilitates high-velocity movements and high-accuracy placements of the object as required during exposure. For certain types of microlithography (notably charged-particle-beam (CPB) and X-ray microlithography systems) the stage(s) must be capable of operation in a high-vacuum environment.
Stage devices for microlithography systems have any of various configurations. Two common configurations are the so-called “H-type” and “I-type” configurations that provide X-Y movements of the object. Both of these types of stage devices include a moving guide bar extending (e.g, in the Y-direction) between two parallel fixed guide bars (extending, e.g., in the X-direction). The actual stage (platform) on which the object is mounted is attached to a “slider” that moves along the moving guide bar. The names of these types of stage devices reflect their respective plan profiles. For example, in the “H-type” stage device the legs of the “H” are defined by the fixed guide bars and the cross member of the “H” is defined by the moving guide bar. In the “I-type” stage device the stem of the “I” is defined by the moving guide bar and the top and bottom caps of the “I” are defined by the fixed guide bars. In most instances, H-type stage devices are used as substrate stages in which possible movements in the X- and Y-directions are relatively “long” strokes. I-type stage devices typically are used as reticle stages in which possible movement along only one of the X- and Y-directions is a relatively long stroke.
Recently, linear motors have been used as actuators in stage devices for imparting motions of the platform in the X- and Y-directions. Linear motors have many advantages such as relative simplicity and compactness of construction, relatively low mass, and high operational efficiency. However, in stage devices as used in CPB microlithography systems (e.g., electron-beam microlithography systems), use of linear motors causes certain problems. Specifically, a linear motor comprises a moving “reaction member” (also called a “rotor” even though it does not rotate) and a stator, one of which comprising a coil extending in both directions along the respective axis, and the other of which having an array of permanent magnets extending in both directions along the respective axis. Whenever a linear motor is used as the actuator of a slider on a moving guide bar, since the moving guide bar itself moves, the entire linear motor carried by the moving guide bar moves as the moving guide bar moves. As this linear motor moves, the array of permanent magnets (whether in the reaction member or in the stator) moves, which causes corresponding magnetic-field fluctuations in the environment of the charged particle beam as the beam is being used for making lithographic exposures. These magnetic-field fluctuations affect the trajectory of the beam, which prevents the beam from achieving a desired pattern-transfer accuracy of several nanometers on the substrate.
Hence, in a CPB microlithography system in which a stage is actuated by a linear motor, especially if the stator comprises the array of permanent magnets and the reaction member comprises the coil, at least the stator must be shielded by a magnetic shield made of a high permeability material. It also is necessary to provide a dynamic magnetic-field-cancellation device in the moving element. Use of shields and field-canceling devices is directed to the fields themselves, and complicates use of these types of stage devices in CPB microlithography systems. Also, shields and field-canceling devices add substantial complexity and cost, and also add substantial mass to the stage devices.
For these reasons, stage actuators that do not rely on electromagnetic fields are in demand for use in stages used in CPB microlithography systems. One type of non-magnetic actuator is a pneumatic cylinder that uses pressurized air or other gas to generate driving force. Unfortunately, use of a pneumatic cylinder in this manner causes stage motions to be non-linear in their manner of control, which requires implementation of an offsetting linearized compensation scheme to achieve satisfactory motion control. In addition, in view of the relationship between flow volume and pressure in the pneumatic cylinder, it is difficult to increase the range over which movements can be controlled accurately, in contrast to use of a linear motor. Hence, other types of non-electromagnetic actuators are needed.
In certain conventional stage devices as used in microlithography systems, long-stroke stage motions have been achieved using ultrasonic linear actuators. Unfortunately, ultrasonic linear actuators generate vibrations, which can cause problems in exposure accuracy and precision. Also, magnetostriction-based actuators have been considered that move a stage in an inchworm “walking” manner (since individual element displacements are very small). In this regard, see Japan Kôkai Patent Document No. Hei 11-178368. However, neither of these approaches has exhibited satisfactory performance to date.